Abstract

We have used a combination of rf and dc excitation to control the plasma density during planar magnetron sputter deposition of CdTefilms and CdTe-based solar cells. While adding dc current we have adjusted the rf power to maintain a constant deposition rate. We find that the lower plasma density obtained with negative dc currents yields films with a more highly faceted surface, more columnar growth structure, and stronger photoluminescence. The solar cells prepared with rf sputteredCdS and with CdTedeposited at reduced rf power and −70 mA of dc current produce substantially higher performance. The results indicate advantages to reducing the ion bombardment energy and flux to the growingfilm by the addition of dc control during rf sputtering from highly insulating semiconductor targets.